The growth of KNSH/KCSH bicrystals from aqueous solutions at a constant temperature difference

•A setup is proposed for growing KNSH/KCSH and KCSH/KNSH/KCSH bulk crystals from aqueous solutions.•It is shown that transmission intensity of crystals is related to defects in the heteroboundary.•KCSH/KNSH bicrystal shows transmission similar to that of mono-component crystals. The setup with a feed zone for growing crystals from aqueous solutions at a constant temperature difference was implemented in this work. It combines feed and growth zones in one block. The capabilities of the setup developed were demonstrated by growing K2Ni(SO4)2·6H2O (KNSH)/K2Co(SO4)2·6H2O (KCSH) bicrystals and KCSH/KNSH/KCSH tricrystals. The influence of initial supercooling and substrate orientation on the inclusions formation at the KCSH/KNSH heteroboundary was studied by X-ray topography. The KCSH/KNSH bicrystal grown at 1 °C initial supercooling on the (1 1 0) KNSH substrate shows 77% transmission that is close to the transmission of mono-component Tutton salts and allows using bicrystals as optical filters of the solar-blind range.